The present invention relates to energy storage devices, and in particular, to using certain materials in the fabrication of the storage device components to mitigate detrimental effects of over-discharging the storage device.
During over-discharge of Li-ion (lithium-ion) batteries, the increase in potential at the negative electrode (anode) can cause cell failure or degradation by oxidizing and dissolving the current collector material. For example, many Li-ion batteries use a negative current collector made of copper. An oxidizing potential of greater than about 3.3 V vs. Li at the anode will cause dissolution, at least to some extent, of the copper current collector.
The following exemplary techniques may be used to mitigate the dissolution of the current collector:                (1) Adding Li2NiO2 to the cathode as over-discharge protection additive. With a low first cycle efficiency, Li2NiO2 reduces first cycle efficiency of the cathode to match with the first cycle efficiency of the anode.        (2) Adding to the cathode materials with a lithiation potential that is lower than 3.5V vs. Li (e.g., LiFePO4, LiMnO2).        
The redox potentials of Li2NiO2 and LiFePO4, however, are 3.6 V to 3.7 V and 3.45 V vs. Li, respectively, which are higher than the dissolution potential of copper. At zero voltage of a Li-ion battery (i.e., when the anode potential equals the cathode potential), copper dissolution may still occur, particularly at elevated temperature (e.g., at or above 60° C.).